1. Field of the Invention
This invention relates to an alkyl iodide storage container which uses in the contact surface between the alkyl iodide liquid and gas inside the container a stabilizing material for repressing decomposition of the alkyl iodide, thereby preventing the container from corrosion and enabling the alkyl iodide to be stably stored for a long time without incurring deterioration and to a method for purifying an alkyl iodide by the use of this storage container.
2. Description of the Related Art
Alkyl halides are compounds in extensive industrial use for raw materials of chemical products, solvents, and fumigants. Methyl iodide which has one carbon atom, for example, has a low boiling point and is used as fumigants for soil, timbers, agricultural produces, buildings, structures, and cultural assets and can exist in a gaseous state at room temperature. The alkyl halides, depending on the kind of alkyl group, may exist in a liquid state at room temperature. The containers used for storing the alkyl halides, therefore, come in various types to suit such varying states of existence. Particularly, some of the alkyl halides are used as fumigants as described above and they possess no insignificant toxicity. Thus, pressure-resistance containers or cylinders made of glass or high pressure-resistance containers or cylinders made of metal or normal pressure metallic containers are being used to avoid leakage of such alky halides during the course of storage and transportation.
It is well known that alkyl iodide can release iodine when it is exposed to such factors as even slight light and the state of storage. For example, the alkyl iodide (RI) (wherein R denotes an alkyl group) reacts with water and generates iodine (I2) and an alcohol (ROH). The iodine is a dark brown gaseous substance and, when suffered to dissolve in the alkyl iodide, causes coloration to the product. The inclusion of free iodine in the alkyl iodide results in not only deteriorating the product itself but also inducing corrosion of the metals used in the container and the vaporizer, and further causing leakage through the container by penetration and inflicting unexpected toxic harm on the substance being fumigated. The prevention of the alkyl iodide from being deteriorated during the course of storage and/or transportation thereof in the container and the protection of the container itself, therefore, have been promoted as by furnishing the container with a packing made as of polytetrafluoroethylene which is capable of preventing leakage of the generated iodine thereby ensuring air tight of the container, lining inside the container with polytetrafluoroethylene in order to prevent metallic parts of the container from the corrosion by the iodine, and placing such a stabilizing agent as hypo water in the container to trap the generated iodine.
Even if a container which is provided at the design stage with sufficient corrosion-resistant and airtightness is put to use, more often than not the iodine generated in consequence of decomposition corrodes the container structured with the metal, or promotes deterioration of the packings, and ultimately leaks from the container and deprives of the container of its airtightness. As reasons for this decomposition of the alkyl iodide, the light and the heat during the alkyl iodide is introduced into the container or during its storage in the container and the oxide adhered to the inner wall surface of the container may be cited. Since perfect elimination of these causes is next to impossible, the causes results in the service life of the container being shortened.
The method for coating a polytetrafluoroethylene on the inner wall surface of the container entails the difficulty in cleaning the interior of the container because the container of a closed structure. Even the addition of such a stabilizing agent as a radical scavenger or a hypo water fails to manifest their effect fully satisfactorily when corrosion occurs in the gas phase. Further, the addition of the stabilizing agent, depending on the purpose of use, is possibly at a disadvantage in lowering the purity of the alkyl iodide.